Resonance type optical deflecting devices having been proposed so far have the following advantageous features, as compared with optical scanning optical systems using a rotary polygonal mirror such as a polygon mirror: that is, the optical deflecting device can be made small in size; the electric power consumption is slow; and theoretically there is no surface tilt of the mirror surface.
On the other hand, since in the resonance type deflectors, in principle, the deflection angle (displacement angle) of the mirror changes sinusoidally and thus the angular speed is not constant. A technique for correcting such characteristic is disclosed in U.S. Pat. No. 7,271,943.
More specifically, U.S. Pat. No. 7,271,943 shows a microoscillator in which a system comprising a plurality of torsion springs and a plurality of movable elements has a plurality of discrete natural oscillation modes. In this microoscillator, the discrete natural oscillation modes include a reference oscillation mode which is a natural oscillation mode having a reference frequency and an even-multiple oscillation mode which is a natural oscillation mode having a frequency approximately an even-number-fold of the reference frequency. In U.S. Pat. No. 7,271,943, the microoscillator is oscillated with these oscillation modes by which sawtooth wave drive or the like is realized. Here, the sawtooth wave drive refers to such drive that, as shown in FIG. 4, during one period of the reciprocal motion of a movable element, the displacement time in the forward stroke differs from the time in the backward stroke.
Furthermore, U.S. Pat. No. 5,347,124 shows a system in which the deflection angle and its peak value of a reflecting mirror of an optical deflector are detected, and a driving signal of the optical deflector is controlled based on these. More specifically, a variable resistance element of a differentiating circuit which constitutes a PID operating circuit is adjusted to thereby optimize the amplitude of the reflecting mirror of the resonance type optical deflector and the vibrational state thereof.